title: Fluorescent zinc(II) complex exhibiting "on-off-on" switching toward Cu2+ and Ag+ ions.
abstract: Binuclear zinc(II) and copper(II) complexes based on a new Schiff base ligand N,N'-bis(2-hydroxybenzilidene)-2,4,6-trimethylbenzene-1,3-diamine (H(2)L) have been synthesized. The ligand H(2)L and complexes under investigation have been characterized by elemental analyses, spectral (FT-IR, (1)H, (13)C NMR, ESI-MS, electronic absorption, emission), and electrochemical studies. The structures of H(2)L and complexes [{Zn(C(23)H(18)N(2)O(2))}(2)] (1) and [{Cu(C(23)H(18)N(2)O(2))}(2)]·H(2)O (2) have been determined crystallographically. Selective "On-Off-On" switching behavior of the fluorescent complex 1 has been studied. The fluorescence intensity of 1 quenches (turns-off) upon addition of Cu(2+), while enhances (turns-on) in the presence of Ag(+) ions. The mechanisms of "On-Off-On" signaling have been supported by (1)H NMR, ESI-MS, electronic absorption, and emission spectral studies. Job's plot analysis supported 1:1 and 1:2 stoichiometries for Cu(2+) and Ag(+) ions, respectively. Association and quenching constants have been estimated by the Benesi-Hildebrand method and Stern-Volmer plot. Moreover, 1 mimics a molecular keypad lock that follows correct chemical input order to give maximum output signal.
authors.affiliation: Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi-221 005 (U.P.), India.
authors.forename: Rampal
authors.initials: R
authors.lastname: Pandey
authors.forename: Prashant
authors.initials: P
authors.lastname: Kumar
authors.forename: Ashish Kumar
authors.initials: AK
authors.lastname: Singh
authors.forename: Mohammad
authors.initials: M
authors.lastname: Shahid
authors.forename: Pei-zhou
authors.initials: PZ
authors.lastname: Li
authors.forename: Sanjay Kumar
authors.initials: SK
authors.lastname: Singh
authors.forename: Qiang
authors.initials: Q
authors.lastname: Xu
authors.forename: Arvind
authors.initials: A
authors.lastname: Misra
authors.forename: Daya Shankar
authors.initials: DS
authors.lastname: Pandey